Heretofore, fused silica has been used to form refractory ceramic components requiring high dimensional stability, low thermal expansion and good strength retention properties, such components as blow pipe liners, runners for iron blast furnaces, and furnace lining and brick being well known applications. The common method for forming such components is thixotropic casting or slip casting in which the fused silica is formed into a slip which is poured into forming molds followed by drying and high temperature firing. This method is suitable for low volume production but not where high volume is required.
Typical of such applications is the composition and method disclosed in U.S. Pat. No. 3,488,723 issued to F. M. Veazie Jan. 6, 1970 covering the formation of a combination manifold-muffler liner. The patentee here discloses the use of a coarse grained mixture of fused silica and glass together with bentonite and water for pressing or casting to a desired shape. The patentee does not disclose or teach the need for controlling alkali and alkaline earth content for preservation of the low coefficient of thermal expansion but instead teaches the manipulation of grain size using materials having a coefficient as high as 6.times.10.sup.-6 /C.degree. and uses a soda-lime glass as a binder.
The patent to G. H. Criss U.S. Pat. No. 3,770,867 issued Nov. 6, 1973 discloses the use of coarse grained fused silica together with volatilized silica and a plasticizing organic binder to enable extrusion of the mixture, the amounts of organic binder varying from 0.25 to about 3% by weight and the volatilized silica from about 1-15% by weight, the desired shapes being formed as the extrudate.
With reference to the limitation of the amount of total alkali and alkaline earth content, the patent of G. F. Carini et al U.S. Pat. No. 3,791,835 issued Feb. 12, 1974 discloses a mixture comprised principally of quartz (crystalline) wherein the total alkali metals content is limited to 0.2% by weight. Similarly, the patent to I. M. Lachman et al U.S. Pat. No. 3,885,977 issued May 27, 1975 discloses the limitation of the amount of alkali metal content to less than 0.4% by weight and the calcium content to less than 0.1% by weight, the composition being cordierite having anisotropic crystal orientation. In each of these disclosures, the patentee is attempting to prevent crystalline materials from transforming.